Backlights of large-screen LCD panels use a large number of light-emitting diodes (LED) often connected in series strings. Wiring of these strings is typically extensive, and an inadvertent electrical contact sometimes occurs in assembly between one of the LED string taps and the metal chassis. Usually, the current feedback is derived at the cathode terminal of the LED string, and it is referenced to the chassis potential as well. Hence, such an inadvertent contact causes a loss of the current feedback signal.
Such a defect is difficult to detect in production, since the LEDs remain lit, although possibly powered by increased current. Hence, this defect could potentially cause damage to the LED backlight. Protection from this short circuit condition usually requires sensing the LED current at a high-voltage potential, associated with the forward voltage drop across the LED string. Such approach requires a relatively expensive high-voltage signal level translator circuit that is not well-suitable for integration with the LED driver control IC.
Therefore, it would be desirable to provide a circuit and method that overcomes the above problems. The circuit may be a fully ground-referenced protection circuit that would be able to reduce the backlight cost and component count.